In an electrical system maximum power transfer between a load and a source is achieved when impedances of the load and the source are matched with respect to each other, which minimizes reflection losses between the load and the source. In many electrical devices the source is a power amplifier and the load can be e.g. an antenna or a line transformer. For example, in a mobile communication device an antenna impedance varies considerably with frequency and with external circumstances causing impedance mismatch between the antenna and a power amplifier feeding the antenna. An example of an external circumstance that has an effect on the antenna impedance is positions of user's fingers in the vicinity of an antenna, i.e. an ‘finger effect’. In a mobile communication device an antenna impedance can vary over a wide range, characterized by a voltage standing wave ratio (VSWR) reaching up to 10:1. For a power amplifier of a transmitter, impedance mismatch has an adverse impact on power losses, maximum reachable output power, and linearity. Impedance mismatch may also change frequency responses of duplexer filters, as high-quality-value (high-Q) filters are very sensitive to changes in their load and supply impedances. Because of the above-mentioned reasons, there is a need for impedance matching between a source and a load.